Distinctive features of female-to-male transsexualism and prevalence of gender identity disorder in Japan.

Introduction: The prevalence of transsexualism is thought to differ among socio-geographic backgrounds, and little is known about its prevalence in Japan. Polycystic ovary syndrome (PCOS), which is known to be associated with insulin resistance and metabolic syndrome, is often seen in female-to-male (FTM) transsexual patients. Consequently, detection of PCOS is an important part of health care for these individuals.

Aim: The purpose of this study was to assess the prevalence of transsexuality in Japan, as well as the incidences of PCOS and insulin resistance among Japanese FTM transsexual patients.

Methods: One hundred four male-to-female (MTF) and 238 FTM Japanese transsexual patients were studied. Medical histories, including histories of menstrual cycling and hormone treatment, were taken. To exclude other diseases, such as congenital adrenal hyperplasia and hormone-secreting tumors, thorough medical assessments, including transvaginal or transrectal ultrasonography and measurement of serum hormone levels and insulin resistance indexes, were performed.

Main Outcome Measures: The diagnosis of PCOS was based on the Rotterdam 2003 criteria.

Results: Based on demographic statistics, the prevalences of MTF and FTM transsexuality are about 3.97 and 8.20 per 100,000 people, respectively, making the MTF-to-FTM ratio about 1:2. Of the FTM transsexual patients studied, 128 had not taken hormones before their initial assessment (untreated group); the remaining 50 self-administered androgen. Among the untreated group, 32.0% were diagnosed with PCOS, 30.1% were insulin-resistant, and 31.1% showed hypoadiponectinemia.

Conclusions: The sex ratio among Japanese transsexuals is different than among Caucasians. PCOS and insulin resistance are common findings in FTM transsexual patients at initial presentation.